In the prior art the problem of linearly scanning a flat surface with a light beam is most commonly solved by utilizing a stationary collimated light source, lenses, rotating polygonal mirrors and other oscillating mirrors to deflect the collimated light beam over the flat surface. There are problems with this common approach and it is relatively complex and expensive. For example, multiple lenses are utilized to expand the collimated light beam and then to focus the collimated light beam, as well as to perform other manipulations of the light beam before it is scanned across the flat surface. In addition, a motor drive is typically used to rotate the multi-faced polygonal mirror, which motor is subject to mechanical wear and often has relatively complex circuitry associated therewith to exactly regulate the motor speed.
The position of mirrors and lenses with respect to the rotating polygonal mirror must also be very carefully adjusted to assure that the collimated light beam is caused to impinge upon a reflecting mirror surface disposed parallel to the rotation axis of the reflecting surface of the polygonal mirror from a finite angle with respect to a plane crossing both the rotation axis and the reflecting mirror at right angles therewith. Upon any deviation therefrom, the beam reflected from the polygonal mirror assumes a conical shape which requires further correction.
The prior art multi-faced polygonal mirror that is rotated via a motor and used to reflect the collimated light beam to produce the scanning beam must also be carefully made in order to achieve linear scanning. This is relatively difficult and costly. When the accuracy of dividing the polygonal surfaces used for deflecting the collimated light beam is not high, difficulties arise regarding timing the commencement of scanning. That is, synchronizing the time at which every scanning line should commence. When a modulated scanning beam is deflected by inaccurately finished polygonal surfaces of such a polygonal mirror, the position of each scanning line is displaced relative to the direction of scanning according to the angular error in the associated surface of the polygon. This distortional error is called "jitter". The manufacture of polygonal mirrors having high accuracy is very difficult and particularly for polygonal mirrors having a great number of polygonal surfaces. To increase the accuracy of polygonal mirrors deflection systems, relatively complex circuitry is necessary to time the scanning.